Field of the Invention
The invention relates to a method for controlling an actuator. It relates in particular to an actuator for controlling an internal combustion engine.
A control process for controlling an actuator is disclosed in the commonly assigned U.S. Pat. No. 6,292,345 B1 (international PCT publication WO 99/17009). The actuator has an actuating element which is, for example, in the form of an inlet or outlet valve of an internal combustion engine. Furthermore, the actuator has an actuating drive with two electromagnets, between which an armature plate can in each case be moved against the force of a resetting means by switching off the coil current to the holding electromagnet and by switching on the coil current to the catching electromagnet. The coil current for the respective catching electromagnet is kept constant at a predetermined capture value for a predetermined time period. Then, immediately before the armature plate arrives at the respective contact surface, an increased holding current is set for a further predetermined time period until it is certain that the armature plate is in contact with the contact surface. A free-wheeling process is then switched, during which the current decreases until it reaches a predetermined holding value, at which it is then regulated until the armature plate is intended to be moved back to the other contact surface. The current is then reduced to a zero value.
It is accordingly an object of the invention to provide a method for controlling an actuator, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which ensures that the actuator is driven precisely even with high loads.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling an actuator, the actuator comprising an actuating element and an actuating drive with at least one electromagnet having a coil, and an armature movably disposed between a first contact surface on the electromagnet and a second contact surface, the method which comprises:
conducting an initial current or a relatively higher holding current with a given polarity through the coil until a time at which the armature is reliably in contact with the first contact surface on the electromagnet;
subsequently selecting an operating state of high-speed current reduction, and thereby applying to the coil an opposite polarity of a supply voltage in comparison with the given polarity; and
conducting a holding current through the coil.
In accordance with an added feature of the invention, the operating state of high-speed current reduction comprises charging an electrical energy store from the coil.
In accordance with another feature of the invention, the method is implemented in an internal combustion engine and the actuating element is a gas exchange valve of the internal combustion engine. In this case, as an alternative to the selection of the operating state of high-speed current reduction, the system selects an operating state of free-wheeling when a condition is satisfied which depends on at least one variable represents the load on the internal combustion engine.
In accordance with a preferred feature of the invention, the variable representing the load on the engine is an air mass flow and a speed of the engine.
In accordance with a concomitant feature of the invention, the operating state of high-speed current reduction is selected for a predetermined time period, and the time period is determined as a function of the holding current and the initial current or the relatively higher holding current.
In other words, the invention is distinguished by the fact that the transition from controlling the capture current or the increased holding current in the coil to controlling the holding current takes place by way of an operating state of high-speed current reduction. The holding current is thus reached considerably more quickly than with the method that is known from the prior art. This ensures that, even when an internal combustion engine is operating at very high speeds and the engine load is at the same time low, the actuating elements, which are in the form of intake or outlet valves, can be driven precisely, since the holding current level is reached very quickly. If the coil is then switched off from the holding current level, then the time period (sticking time) which is required before the armature plate is detached from the respective contact surface can thus be determined precisely in advance, since the holding current level is predetermined.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for controlling an actuator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.